This invention relates to a control system for a device for feeding individual sheets to the platen of a printing apparatus.
Devices are presently utilized in which stacks of sheets are stored in one or more storage units, said devices being associated with various types of printing apparatus. Separating means is provided for each storage unit which is driven by the platen of the printing apparatus through various means such as gears, or the like.
Selecting means is interposed in the drive train between the platen of the printing apparatus and the separating means so that a selecting means is provided for each separating means.
The separating means can be provided in the form of a separating roller or equivalent structure and is designed to strip the uppermost sheet of the stacked sheets in a selected storage unit from said stack.
The selecting means determines that only one selected separating means is actuated at a given time and that a sheet is fed to the platen of the printing apparatus from the selected storage unit. The selecting means are controlled mechanically by the platen through the gear train or other drive in that the platen is controlled by a sequence of forward and backward rotary movements which are, in turn, designed to control each selecting means. Consequently, the activation of the separating means, as well as the selection of the respective storage unit, is accomplished by the program-controlled rotation of the platen of the printing apparatus.
In the sheet-feeding device disclosed in U.S. Pat. No. 4,248,415 the selecting means consists of a pawl which is mounted on a pawl disc, whereby the pawl engages a selecting disc which drives the separating means by means of an overrunning clutch drive. A control lever pivotally mounted upon the selecting disc release the pawl from the selecting disc when the associated storage units are not involved in the sheet-feeding process.
In another embodiment of the device disclosed in the '415 patent, the selecting disc is provided with a switching arrangement in the form of a selecting channel extending through the selecting disc and the selecting channel is obstructed at one of its extremities by a leaf-type spring functioning as a switching member. When activating a selected storage unit, the pawl, as the result of the predetermined sequence of forward and backward rotary movements of the platen of the printing apparatus, engages the selecting channel and drives the selecting disc, the selecting disc then driving the separating means constituted by a separating roller through the previously mentioned overrunning clutch.
The pawls of the unactivated storage units pass through the selecting channel in one direction of rotation and emerge from said channel by deflection of the leaf-type spring or are carried away in the opposite direction of rotation over the selecting channel through the operation of the leaf-type spring. In the known devices discussed hereinabove, the selecting means is costly as it requires an overrunning clutch or an overriding freewheel drive.
When the prior art devices disclosed hereinabove are utilized with printing apparatus which imprints the sheet on the platen with mathematical or chemical formulae or with graphical representations, the platen is frequently rotated forward and backward by a few or several line increments and the characteristic control sequence of the forward and backward rotary increments of the platen intended to activate the selecting mechanism or means of an associated storage unit can manifest itself accidentally with the result that the selecting means is accidentally activated unintentionally.
Disclosed in co-pending application Ser. No. 781,792 is a construction wherein the pawl on the driven pawl disc, while being controlled by a selecting disc, engages a toothed disc to establish the driving connection between the platen of the printing apparatus and the selected separating means or roller. In order to prevent the inadvertent operation of the separating means or roller during the imprinting of formulae or graphic representations, the selecting means or devices are locked by a locking device during the printing process and a single revolution coupling driven by the platen of the printing apparatus inactivates the locking device at the end of the printing of the formulae or graphic representations so that the next selecting process can take place.